Monolithic liner and method of construction



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United States Patent MONOLITHIC LINER AND METHOD OF CONSTRUCTION Ernest D. Larson, Orem, and Howard H. Nichols, American Fork, Utah, assignors to United States Steel Corporaflon, a corporation of New Jersey Application April 14, 1954, Serial No. 423,016

4 Claims. (Cl. 266-43) This invention relates to improved liners for burner ports in bottom fired soaking pits and to methods of forming the same.

In the steel making art a soaking pit is a furnace used for heating ingots to their proper rolling temperature, commonly about 2150 to 2450 F. A bottom fired soaking pit has a port in its bottom wall and a gas burner situated therebelow. An upstanding annular refractory liner surrounds this port. Such liners not only are subject to the maximum furnace temperature, but frequently ingots bump them and cause mechanical damage. Consequently liners often must be replaced after relatively short service. Previous liners have been formed either of refractory brickwork or as monolithic bodies. The latter have been preferred because brickwork can be replaced only after the furnace has cooled sufi'iciently for workmen to enter for relatively long periods. Nevertheless previous monolithic liners with which we are familiar have lacked proper mechanical strength at furnace temperatures, and have had a further disadvantage that their refractory bodies contract and their metal casings expand when heated.

An object of the present invention is to provide an improved monolithic port liner which is more refractory, has greater mechanical strength at the temperatures encountered, and is more accurately shaped than previous liners with which we are familiar.

A further object is to provide an improved port liner and method of making the same which facilitate installation and replacement.

A further object is to provide an improved method of making port liners in which minor repairs to the furnace bottom in the vicinity of the liner can be made automatically at the same time the liner is installed.

In accomplishing these and other objects of the invention, we have provided improved details of structure, a preferred form of which is shown in the accompanying drawing, in which:

Figure 1 is a vertical sectional view of a portion of a bottom fired soaking pit which has a partially formed port liner constructed in accordance with our invention, and of a mold used to form this liner; and

Figure 2 is a side elevational view, partly in section, of the completed liner.

Figure 1 shows a portion of a bottom fired soaking pit which includes a bottom wall formed of refractory brickwork, a gas burner 12, and a layer of coke breeze 13 spread over the brickwork. The wall 10 has a port 14 directly above the burner and preferably this port has a venturi portion 15. The remainder of the furnace is not shown, inasmuch as it can be of any standard or desired construction. For more detailed showings of typical furnaces of this type, reference can be made to Morton Patent No. 2,124,888 or to Making, Shapping and Treating of Steel published by United States Steel Corporation, Sixth Edition, pages 599 and 600.

In accordance with our invention, an annular body portion 16 of a port liner is cast in place on the bottom 10.

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2. This body portion is formed of an acid refractory which on a dry basic and excluding incidental impurities consists essentially of the following:

Percent by weight Silica 25 to 40 Calcium aluminate cement 52 to 72 For example, we have successfully used a composition of the following analysis by weight:

Sufiicient water is added to the above composition to make the material readily castable, in accordance with known practices.

In order to cast the liner body in place, a sheet metal mold 17 is placed on the furnace bottom around the port 14. This mold includes an outer shell 18 and a central core shell 19 which is suspended from the outer shell on cross bars and hangers 20. The space between said shells defines an upwardly tapered mold cavity. A pit crane 21 can be used for positioning and removing the mold, which is equipped with lifting eyes 22 and a chain 23 to permit such handling. After the mold is positioned over the port 14, the castable material already described is rammed or poured into the cavity. This material also serves to fill any voids in the brickwork immediately below the mold and thus automatically effects minor repairs thereto. The inner circumference produces an accurately shaped venturi throat. After the liner body 16 has set for a period of 8 to 16 hours the mold 17 is removed, as shown in Figure 1.

Next the outer face of the liner body is covered with a light gauge sheet 24 of ferrous metal. A layer 25 of plastic basic refractory is laid over this sheet. This basic refractory consists essentially of a mixture of chrome ore, magnesite, incidental impurities, and water. On a wet plastic basis the essential components can be approximately as follows:

Percent by weight Chrome ore 30 to 35 Magnesite 12 to 18 For example, we have successfully used a compound of the following analysis by weight:

Percent SiOz 7.67 FeO 20.80 A1203 10.56 MgO 15.50 MazO 0.82 Cr2O 33.20 Moisture 9.65 Colatile matter 1.80

Next the furnace is heated to a minimum temperature of 2250 F., but preferably 2300" F. for about 16 hours without coke breeze on its bottom. The plastic basic layer 25 and the ferrous sheet 24 react With the surface of the acid body 16 to form a layer about 4 inches thick of a ferro-chromo-silicious mass. This mass has a higher melting point than cast steel and a greater mechanical strength than cast iron. It is highly resistant to chemical attack by slag or the like.

When our port liner is installed to replace a worm liner in a heated soaking pit, the burner 12 is extinguished and the old liner is removed with a scraper carried by the pit crane 21 or by striking it with an ingot swung from this crane. Any debris which fails into the burner can be removed through the usual burner clean-out doors, not shown. Any damage to the brickwork aroundthe port is subseguently repaired automatically, asalready'explained. The mold ll' is positioned while the soaking pit is still relatively hot and body 16 cast therein. By the'time this body has set (8 to 16 hours later) the soaking pit has cooled sufficiently for a workman to enter briefly. to installthe ferrous layer 24 and the plastic basic layer 25. Thereafter the burner can be fired and the furnace again heated.

While we have shown and described only a single embodiment of the invention, it is apparent that modifications may arise. Therefore, We do not wish to be limited to the disclosure set forth but only by the scope of the appended claims.

. We claim: 1. A monolithic. liner. for a bottom fired soaking pit burner port comprising an annular body of castable siliceous acid refractory consisting essentially of 25 to 40 percent by weightsilica and 52 to 72 percent by weight calcium aluminate cement, a layer of ferrous sheet metal on the outside oflsaid body, and a layer of plastic basic refractory over said metal layer and containing on a wet plastic basis 30 to 35 percent by weight chrome ore and 12' to 18 percent by weight magnesite, said sheet metal 4% which is the product obtained by covering said body with a layer of ferrous sheet metal, covering said metal layer with plastic basic refractory containing on awet plastic basis 30 to percent by weight chrome ore and 12 to 18 percent by Weight magnesite, and heating the liner to a minimum temperature of 2250 F. for at least 16 hours.

3. A method of making a burner port liner in a bottom fired soaking pit comprising positioning a mold having an annular cavity over the port, filling said cavity with a castablc acid refractory composition, simultaneously filling any voids in the port walls with said composition, setting said composition to form a liner body, removing the mold, covering'the outside of said body with a layer of ferrous sheet metal, covering said metal layer with plastic basic refractory containing chrome ore, and heating the liner to a minimum temperature of 2250 F. for at least 16 hours to fuse said basic compound and said metal layer with the surface of said body and thus form a layer of ferro-chromo-silicious mass over the outside of said body. i 4. A method as defined in claim '3 in which said acid refractory composition consists essentially of 25 to 40 percent by weight silica and 75 to percent by weight calcium aluminate cement, and said basic refractory on a wet plastic basis contains 30 to 35 percent by weight chrome ore and 12 to l8 percent by weight magnesite.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A MONOLITHIC LINER FOR A BOTTOM FIRED SOAKING PIT BURNER PORT COMPRISING AND ANNULAR BODY OF CASTABLE SILICEOUS ACID REFRACTORY CONSISTING ESSENTIALLY OF 25 TO 40 PERCENT BY WEIGHT SILICA AND 52 TO 72 PERCENT BY WEIGHT CALCIUM ALUMINATE CEMENT, A LAYER OF FERROUS SHEET METAL ON THE OUTSIDE OF SAID BODY, AND A LAYER OF PLASTIC BASIC REFRACTORY OVER SAID METAL LAYER AND CONTAINING ON A WET PLASTIC BASIS 30 TO 35 PERCENT BY WEIGHT CHROME ORE AND 